Photographic emulsions typically comprise silver halide particles dispersed in an aqueous medium. Traditionally, various types of gelatin have been used as a peptizer for the precipitation of photographic silver halide emulsions. This results in a layer of adsorbed gelatin surrounding each silver halide grain. The hydrated thickness of the gelatin layer may vary anywhere from 10 to 60 nm. Silver halide particles comprising silver halide grains each surrounded by a layer of peptizing gelatin are referred to herein as "silver halide-gelatin particles".
Photographically useful compounds, such as filter dyes, development inhibitor releasing couplers, development inhibitor anchimeric release couplers, dye-forming couplers, nucleators, ultraviolet radiation absorbing materials, development accelerators (sometimes referred to as boosters in the art), developers, sensitizing dyes, and the like can be incorporated into photographic emulsions. Typically such photographically useful compounds are added to an emulsion in the form of oil-in-water dispersions resulting in a photographic composition comprising silver halide particles and dispersed droplets comprising the photographically useful compound.
Conventional color photographic elements comprise a plurality of layers coated on a support. In such a photographic element there is at least one color sensitive layer for each of the colors red, green and blue. Mixed-layer color photographic systems have been proposed. A mixed-layer color photographic system is one in which a single photographic layer is made up of silver halide grains with different spectral sensitizations. The manufacturing benefit of such a system is clear: reduction of the number of layers in a color photographic system. The ability to collapse (reduce the number of) differently sensitized layers (different by color or by speed) can lead to cost savings.
There are two kinds of mixed-layer color photographic systems. The system in which differently sensitized silver halide emulsion grains are mixed together in a single layer without incorporation of the corresponding image-forming dye components (often referred to in the art as couplers) is generally called a mixed-grain coating.
The second type of mixed-layer system also contains differently sensitized silver halide emulsion particles but in addition contains different image-forming dye components associated with the silver halide sensitized for each region of the spectrum. The particles that are mixed may or may not be individual silver halide grains. In many coatings of this kind, silver halide grains of a certain sensitivity and the appropriate image-forming dye or dye component are both dispersed in a colloidal vehicle; this vehicle with its contents is then dispersed as globules in a continuous phase or "matrix" consisting of a second colloid vehicle not compatible with the first. A mixture of two or more such dispersions containing particles of different spectral sensitivity is commonly called a mixed-packet coating. However, there are other materials in which image-forming dyes or dye components are intimately associated with the color-sensitized silver halide grains themselves, as by adsorption or complex formation, and the grains are mixed in a single emulsion vehicle. Such materials are also considered mixed-packet materials.
The processing of mixed-packet materials is usually simpler than that of mixed-grain materials. This is the result of associating the proper image-forming dye or dye component with the silver halide sensitized for each region of the spectrum. A single chemical step can suffice, therefore, to form all the dye images, each under the control of the proper set of silver or silver halide grains. On the other hand, mixed-grain materials usually require not only the original exposure to the subject, but also two or more reversal exposures to light of different colors, each followed by a reversal development in a different color developer solution containing a soluble coupler to introduce the three dye components one after another and to form the three dye images, each under the control of the proper set of differently sensitized grains.
Because of the potential commercial value of an acceptable quality mixed-packet system, extensive work has been done as indicated in the prior art references U.S. Pat. Nos. 2,698,796 to Chechak et al., 2,698,797 to Godowsky et al., 2,763,552 to Van Campen et al., 2,965,484 to Tulagin et al., 2,698,794 to Godowsky, and 4,865,940 to Schranz (RA-16 through RA-21). However, none of the prior art mixed-packet systems has achieved commercial success.
Our copending application Ser. No. 08/1,361 filed Jan. 7, 1993 (RA-30), the disclosure of which is incorporated herein by reference, describes the precipitation of Ag-halide emulsions in the presence of gelatin-grafted-polymer particles comprising a photographically useful compound. By the method disclosed in this copending application one obtains polymer particles directly attached to the Ag-halide microcrystals. As elucidated in RA-30, there are many advantages associated with having such polymer particles attached to silver halide grains in emulsion systems, including the preparation of mixed packet photographic systems. However, the method described in this patent application requires modification of known emulsion preparation processes to optimize the process for use with the gelatin-grafted-polymer particles.
PROBLEM TO BE SOLVED BY THE INVENTION
There is a need to improve delivery of photographically useful compounds to silver halide particles in a photographic emulsion without having to modify and/or optimize conventional emulsion forming processes. In particular, there is a need to improve delivery of photographically useful compounds to specifically sensitized silver halide particles specific to the spectral sensitivity of the silver halide particles in order to form mixed-packet color photographic systems.